The present invention relates to cementing operations and, more particularly, in certain embodiments, to geopolymer cement compositions comprising slag and pumice and associated methods use in cementing operations.
In cementing operations, such as well construction and remedial cementing, cement compositions are commonly utilized. Cement compositions may be used in primary-cementing operations whereby pipe strings, such as casing and liners, are cemented in well bores. In a typical primary-cementing operation, a cement composition may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe string disposed therein. The cement composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable material (e.g., a cement sheath) that may support and position the pipe string in the well bore and may bond the exterior surface of the pipe string to the well bore walls. Among other things, the cement sheath surrounding the pipe string should function to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Cement compositions also may be used in remedial cementing methods, such as in the placement of plugs, and in squeeze cementing for sealing voids in a pipe string, cement sheath, gravel pack, subterranean formation, and the like. Cement compositions also may be used in surface applications, for example, in surface applications.
A particular challenge in cementing operations is the development of satisfactory mechanical properties in a settable composition within a reasonable time period after placement in the subterranean formation. During the life of a well, the subterranean cement sheath undergoes numerous strains and stresses as a result of temperature effects, pressure effects, and impact effects. The ability to withstand these strains and stresses is directly related to the mechanical properties of the settable composition after setting. The mechanical properties are often characterized using parameters such as compressive strength, tensile strength, Young's Modulus, Poisson's Ratio, elasticity, and the like. These properties may be modified by the inclusion of additives.
One type of settable composition that has been used heretofore comprises slag cement, which is typically a blend of Portland cement and slag. Because Portland cement develops compressive strength much more rapidly than slag, the amount of slag is typically limited to no more than 40% by weight of the slag cement. Drawbacks to slag cement include the relatively high cost of the Portland cement as compared to the slag, which is a waste material. Drawbacks to using higher concentrations of slag may include the inability for the settable composition to develop adequate compressive strength in a reasonable time and ensure the long-term structural integrity of the cement.
Thus, there exists a need for cement compositions that comprise slag with enhanced mechanical features that develop adequate compressive strength for use in cementing operations.